The Perfection of Quartz and Other Crystals and Its Relation to Surface Treatment

Abstract

The perfection of various crystals has been determined by using an x-ray double crystal spectrometer. The materials examined were quartz, Rochelle salt, fluorite, tourmaline, pyrites, barite, rocksalt, gypsum, and the metallic crystals aluminum, iron, nickel, tungsten, and permalloy (65 percent nickel). The results indicate that quartz is a "perfect" crystal and that specimens of Rochelle salt, fluorite and possibly tourmaline and pyrites, might be found which could be so classed. The others tested are definitely in the "imperfect" class, the widths of the rocking curves at half-maximum lying between 100 and 1500 seconds of arc. The effect of surface treatment on perfection, as determined by x-rays, was examined for quartz by grinding with carborundum of two different sizes and by etching for different lengths of time. The surface of the permalloy crystal was also investigated by etching to different depths. As a result of the tests here reported, etched quartz crystals are suggested as suitable for use in the double crystal spectrometer on account of their high resolving power which is about twice that of calcite.